Fraud investigators had been attempting to trace assets belonging to SLS Capital, a Luxembourg company controlled by the entrepreneur David Elias, following the collapse of Keydata more than three years ago. Mr Elias, who fled to Singapore, died in 2009.

It transpired that £103 m of life insurance policies that were managed by SLS Capital and sold to investors as so-called death bonds had disappeared. The FSA referred the business to the SFO, while PwC was appointed as Keydata's administrators.

"Substantial efforts have been made to trace the assets of SLS Capital SA and David Elias in overseas jurisdictions since September 2010. These efforts have not met with any success and it is considered unlikely that the situation will change," the SFO said on its website last night.

"Accordingly, the SFO is closing this case and will not be pursuing any further enquiries in relation to this matter."

The SFO, which had been looking into Keydata since July 2009, announced in April last year it had found "insufficient evidence" to secure a prosecution, following a review of the case. It said at the time that it would concentrate on tracing SLS Capital assets instead of attempting a prosecution.